A crystalline-resin blow molded product excellent in surface gloss, high in surface hardness and hard to be scratched; and its efficient production method. A method of producing a blow molded product by blow-inflating a crystalline-resin molten parison in a mold, where a temperature around the molding surface of a mold when a parison is supplied is kept within a range of at least a temperature 20 DEG C lower than a crystallizing temperature of the resin to less than a temperature 5 DEG C lower than a melting temperature of the resin, then a pressurized fluid is blown in after the parison is held by molds by clamping to heat the molding surface of the mold to within a temperature range of a temperature 10 DEG C lower than a melting temperature of the resin to a temperature lower than the melting temperature, time-retention required to produce a molded product with a surface hardness of a pencil hardness of HB or higher is effected within that temperature range, and a molding mold is cooled and demolded. A crystalline-resin blow molded product obtained by this production method has a surface glossiness of 80% or higher and a surface scratching property of a pencil hardness of HB or higher.